Method of forming a magnetic device having a conductive clip

ABSTRACT

A method of forming a magnetic device by providing a conductive substrate and placing a magnetic core proximate the conductive substrate with a surface thereof facing the conductive substrate. The method also includes placing a conductive clip proximate a surface of the magnetic core and electrically coupling ends of the conductive clip to the conductive substrate to cooperatively form a winding therewith about the magnetic core.

TECHNICAL FIELD

The present invention is directed, in general, to electronic devicesand, in particular, to magnetic devices and power modules, and relatedmethods of forming the same.

BACKGROUND

Magnetic devices such as inductors are often used in circuit design forelectronic devices (e.g., power modules) in which energy is stored in amagnetic field surrounding an electrically conductive element such as acoil of copper wire. To produce an inductor that can store a usefulamount of energy for a given size and a given current level, a number ofelectrically conductive turns or wires are formed around a magneticstructure or core such as a layer of magnetic material. The magneticfield is enhanced by the permeability of the magnetic material and bythe presence of the multiple conductive turns. As the size of electronicdevices has been reduced by using integrated circuits and printed wiringboards with surface mount assembly techniques, the size of inductors hasnot, to date, decreased proportionately.

Attempts to use finer wire sizes have resulted in inductor designs withlimited current handling capability. Silver is recognized as a slightlybetter conductor than copper for higher current levels, but its expenseis generally not warranted in practical products. These effects havecombined to make the design of magnetic devices a continuing object forfurther size and cost reductions without compromising the respectivecurrent ratings.

A number of approaches beyond the use of finer copper wire have beenused in the past to produce smaller inductors. For instance, U.S. Pat.No. 6,094,123 entitled “Low Profile Surface Mount Chip Inductor,” toApurba Roy, issued Jul. 25, 2000 and U.S. Pat. No. 5,802,702 entitled“Method of Making a Device including a Metallized Magnetic Substrate,”to Fleming, et al., issued Sep. 8, 1998, which are incorporated hereinby reference, disclose magnetic devices that form recesses in a bar ofmagnetic material for conductors and deposit conductive material in therecesses. Additionally, U.S. Pat. No. 5,574,420 entitled “Low ProfileSurface Mounted Magnetic Devices and Components Therefor,” to Roy, etal., issued Nov. 12, 1996, which is incorporated by reference, disclosesa magnetic device that forms conductive pathways in a body of magneticmaterial, adds windings by inserting staple-like conductive piece partsthrough apertures in the body, and solders the staples to a patternedprinted wiring board placed below a ceramic magnetic bar to complete thewinding structure. Each of the magnetic devices disclosed in theaforementioned references suffer from a current limitation therefor,which is an impractical design and manufacturing approach for a massmarket. The aforementioned magnetic devices also provide inadequate heatdissipation capability or reduction in the size thereof.

Thus, the designs for the magnetic devices in the past are inadequate toproduce a sufficiently miniaturized magnetic device with a substantialcurrent rating for application in compact devices such as high densitypower converters embodied in power modules. The power converters oftenemploy magnetic devices that can sustain currents exceeding one ampereand are operable at switching frequencies that exceed one megahertz.Additionally, the magnetic devices should exhibit very low electricalresistance at the switching frequency and should be more compact thanpresently achievable designs. The design of power converters isinadequately served by these aforementioned limitations of presentmagnetic devices. In addition, a magnetic device integrable withmanufacturing processes of the commensurate end product such as a powermodule would provide substantial cost savings therefor.

Accordingly, what is needed in the art is a magnetic device, and relatedmethod of forming the same, that can meet the more stringentrequirements of present applications such as compact, efficient and highdensity power modules, while being manufacturable at high volume andwith lower cost than is achieved with the prior art.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by advantageous embodimentsof the present invention which includes a method of forming a magneticdevice by providing a conductive substrate and placing a magnetic coreproximate the conductive substrate with a surface thereof facing theconductive substrate. The method also includes placing a conductive clipproximate a surface of the magnetic core and electrically coupling endsof the conductive clip to the conductive substrate to cooperatively forma winding therewith about the magnetic core.

In another aspect, the present invention provides a method of forming amagnetic device by providing a patterned, conductive leadframe andadhering a magnetic core formed from a bar of magnetic material to theconductive leadframe. The method also includes placing at least oneconductive clip above the magnetic core and soldering ends of the atleast one conductive clip to the conductive leadframe to cooperativelyform a winding therewith about the magnetic core.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1 and 2 illustrate isometric views of an embodiment of anelectronic device, before encapsulation, constructed according to theprinciples of the present invention;

FIG. 3 illustrates an isometric view of an embodiment of an electronicdevice, after encapsulation, constructed according to the principles ofthe present invention; and

FIG. 4 illustrates a diagram of an embodiment of a power converterincluding power conversion circuitry constructed according to theprinciples of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferredembodiments in a specific context, namely, a magnetic device, anelectronic device (e.g., a power module) and a method of manufacturethereof. As the size of magnetic devices continues to shrink, themagnetic devices are also referred to as micromagnetic devices. For thepurposes of the present invention, the terms may be used synonymously.While the principles of the present invention will be described in theenvironment of a power module, any application that may benefit from amagnetic device as described herein is well within the broad scope ofthe present invention.

As will become more apparent, a magnetic device embodied in an inductoris formed with a magnetic core (e.g., a bar of magnetic material)proximate (e.g., above) a conductive substrate (e.g., an electricallyconductive leadframe), and a conductive clip positioned proximate (e.g.,above) the magnetic core to complete a winding thereabout (e.g.,around). Thus, a surface (e.g., a lower surface) of the magnetic corefaces (e.g., generally oriented toward) the conductive substrate and asurface (e.g., an upper surface) of the magnetic core faces (e.g.,generally oriented toward) the conductive clip. As described herein, themagnetic core is formed of a medium that generally conducts a givenmagnetic flux level for a lower level of applied magneto-motive force,such as measured in ampere-turns, compared to a non-magnetic medium suchas air (or a vacuum). The magnetic core may occupy a closed flux pathsuch as provided by a torroidal structure, or may occupy a portion of aflux path such as provided by a flat or round bar of magnetic material.The magnetic core includes structures such as bars and rods, as well asfilms, and may include multiple layers including intervening layers andlayers that improve the magnetic properties thereof.

In addition to the magnetic device, an electronic device such as a powermodule includes other integrated circuits (either in bare die or moduleform) and surface-mount components coupled (e.g., adhesively mounted) tothe conductive substrate and electrically coupled thereto with wirebonds. An encapsulant such as plastic molded material is placed aroundthe magnetic device, integrated circuit and/or the surface-mountcomponents. The power module may also include a power conversioncircuitry that includes or may be embodied in the magnetic device, theintegrated circuit, and at least one surface-mount component. It shouldbe understood that the power module may form, at least in part, a powermanagement system, which itself is often referred to as a powermanagement integrated circuit.

Referring initially to FIGS. 1 and 2, illustrated are isometric views ofan embodiment of an electronic device (e.g., power module), beforeencapsulation, constructed according to the principles of the presentinvention. The power module includes a magnetic device (e.g., inductor),an integrated circuit and surface-mount components. The power module mayinclude power conversion circuitry that includes or may be embodied inthe magnetic device, the integrated circuit and at least one of thesurface-mount components. The power conversion circuitry may form apower converter that often includes switching regulators such as buckswitching regulators with digital control circuits for reduced componentcount, and synchronous rectifiers for high power conversion efficiency.Of course, the broad scope of the present invention is not limited to apower module, power converter or the like, and may be applicable toother electronic devices.

A conductive substrate (e.g., conductive leadframe or leadframe) 110 ispatterned and etched to form an electrically conductive interconnectlayer for the lower portion of a winding for the inductor as well as theelectrical interconnections among surface-mount components, theintegrated circuit, and the inductor. A typical thickness of theleadframe 110 is about eight mils. While the leadframe 110 is oftenconstructed of copper, alternative electrically conductive materials canbe used therefor. The leadframe 110 provides external connections forthe power module, as well as a support base for a magnetic material forthe inductor. The external connections are formed as fingers of theleadframe 110, referenced as leadframe fingers (two of which aredesignated 115, 116).

The leadframe 110 is generally constructed with an integral stripsurrounding the electrically conductive pattern to provide mechanicalsupport during the manufacturing steps, which strip is discarded laterin the manufacturing process. The surrounding strip is generally shearedoff after the electronic device has been constructed. The leadframe 110is generally produced in an array of repeating of patterns (not shown),such as a 16×16 array, to form, for example, 256 substantially identicalelectronic devices. Forming an array of leadframes 110 is a process wellknown in the art to reduce the manufacturing cost of producing theelectronic devices.

Solder paste is selectively applied to the leadframe 110 in a thin layerto areas (one of which is designated 125) for screening processes, toprovide electrical and mechanical attachment for surface-mountcomponents. The surface-mount components such as capacitors (one ofwhich is designated 120) are placed with their conductive ends in thesolder paste. The solder paste may be composed of lead-based as well aslead-free compositions. The array of leadframes 110 with thesurface-mount components 120 is reflowed in an oven to mechanically andelectrically attach the surface-mount components 120 to the leadframe110.

The steps as described above generally do not require execution in thehighly controlled environment of a clean room. The following steps,however, are preferably performed in a clean room environment such astypically used for assembly of integrated circuits into a molded plasticpackage, as is generally well known in the art.

An adhesive (e.g., a die attach adhesive such as Abletherm 2600AT byAblestik of Rancho Dominquez, Calif.) is dispensed onto the leadframe110 to hold a magnetic core (e.g., a bar of magnetic material) 130 andan integrated circuit in the form of a semiconductor die 140. The bar ofmagnetic material 130 and the semiconductor die 140 are positioned onthe leadframe 110 over the die attach adhesive. Thus, a lower surface ofthe bar of magnetic material 130 faces, and is preferably adhered to,the leadframe 110. The bar of magnetic material 130 is included toenhance the magnetic properties of the inductor and may be about 250micrometers (μm) thick, four mils wide and 7.5 mils long. The adhesiveis cured, typically in a controlled thermal process, to secure the barof magnetic material 130 and the semiconductor die 140 to the leadframe110.

Solder paste is applied to areas (generally designated 160) of theleadframe 110 wherein ends of conductive clips 150 are placed. Again,the solder paste may be composed of lead-based as well as lead-freecompositions. The conductive clips 150 (e.g., about 8-12 mils thick) areplaced on the leadframe 110 above the bars of magnetic material 130 withtheir ends in the solder paste. The conductive clips 150 are formed withtheir ends bent toward the leadframe 110 about ends of the bar ofmagnetic material 130 without mechanical interference. Thus, an uppersurface of the bar of magnetic material 130 faces the conductive clips150. An insulating gap, for example, about a five mil air gap, is thuspreferably left between the upper surfaces of the bars of magneticmaterial 130 and the lower surfaces of the conductive clips 150, whichgap may be filled later by an encapsulant. The conductive clips 150provide the portion of the electrically conductive inductor windingabove each bar of magnetic material 130. The leadframe 110 is heated ina reflow oven to mechanically and electrically bond the conductive clips150 to the leadframe 110.

Wire bonds preferably formed of gold wire such as a first wire bond 165are attached to each semiconductor die 140 and to the leadframe 110 toelectrically couple pads on the semiconductor die 140 to bonding areasof the leadframe 110 thereby providing electrical circuit connectionstherebetween. Wire bonds such as a second wire bond 166 may also be usedto selectively electrically couple portions of the leadframe 110 toprovide circuit interconnections that cannot be easily wired in a singleplanar layout, thus producing the topological layout equivalent for theleadframe 110 of a two-layer printed wiring board or substrate.

When the electronic devices are formed in an array as mentioned above,the array is placed in a mold, and an encapsulant such as a moldingmaterial, preferably epoxy, is deposited (e.g., injected) thereover asis well known in the art to provide environmental and mechanicalprotection as well as a thermally conductive covering to facilitate heatdissipation during operation. Other molding materials and processes aswell as electronic devices constructed without an encapsulant are wellwithin the broad scope of the present invention.

The individual electronic devices are singulated from the array thereofby a punching and shearing operation to produce an encapsulated powermodule including power conversion circuitry as illustrated with respectto FIG. 3. The power module is mechanically and hermetically protectedby the encapsulant 170 as illustrated. External electrical connectionsto a system employing the power module are made via terminals 180 whichare created from exposed leadframe fingers (see FIG. 1) protruding fromsides and a lower surface of the power module after encapsulation.Typically, the terminals 180 are substantially coplanar with the sidesand lower surface of the power module. The terminals 180 are formed bythe shearing and molding operation on the leadframe 110 as is well knownin the art.

Electrical connections to the system employing the power module are madeby placing the power module on another circuit board or printed wiringboard formed with interconnect pads that are covered with solder paste,generally by a screening operation, and heating the power module on thecircuit board in a reflow oven. The reflow soldering operation isgenerally also adequate to provide mechanical attachment of the powermodule to another printed wiring board, but other attachment methodssuch as adhesive compound are well within the broad scope of the presentinvention.

Turning now to FIG. 4, illustrated is a diagram of an embodiment of apower converter including power conversion circuitry constructedaccording to the principles of the present invention. The powerconverter includes a power train 410, a controller 420 and a driver 430,and provides power to a system such as a microprocessor. While in theillustrated embodiment, the power train 410 employs a buck convertertopology, those skilled in the art should understand that otherconverter topologies such as a forward converter topology are wellwithin the broad scope of the present invention.

The power train 410 preceives an input voltage V_(in) from a source ofelectrical power (represented by a battery) at an input thereof andprovides a regulated output voltage V_(out) to power, for instance, amicroprocessor at an output thereof. In keeping with the principles of abuck converter topology, the output voltage V_(out) is generally lessthan the input voltage V_(in) such that a switching operation of thepower converter can regulate the output voltage V_(out). A switch (e.g.,a main switch Q_(mn)) is enabled to conduct for a primary interval(generally co-existent with a primary duty cycle “D” of the main switchQ_(mn)) and couples the input voltage V_(in) to an output filterinductor L_(out). During the primary interval, an inductor currentI_(Lout) flowing through the output filter inductor L_(out) increases asa current flows from the input to the output of the power train 410. Acomponent of the inductor current I_(Lout) is filtered by the outputcapacitor C_(out).

During a complementary interval (generally co-existent with acomplementary duty cycle “1-D” of the main switch Q_(mn)), the mainswitch Q_(mn) is transitioned to a non-conducting state and anotherswitch (e.g., an auxiliary switch Q_(aux)) is enabled to conduct. Theauxiliary switch Q_(aux) provides a path to maintain a continuity of theinductor current I_(Lout) flowing through the output filter inductorL_(out). During the complementary interval, the inductor currentI_(Lout) through the output filter inductor L_(out) decreases. Ingeneral, the duty cycle of the main and auxiliary switches Q_(mn),Q_(aux) may be adjusted to maintain a regulation of the output voltageV_(out) of the power converter. Those skilled in the art shouldunderstand, however, that the conduction periods for the main andauxiliary switches Q_(mn), Q_(aux) may be separated by a small timeinterval to avoid cross conduction therebetween and beneficially toreduce the switching losses associated with the power converter.

The controller 420 receives a desired characteristic such as a desiredsystem voltage V_(system) from an internal or external source associatedwith the microprocessor, and the output voltage V_(out) of the powerconverter. The controller 420 is also coupled to the input voltageV_(in) of the power converter and a return lead of the source ofelectrical power (again, represented by a battery) to provide a groundconnection therefor. A decoupling capacitor C_(dec) is coupled to thepath from the input voltage V_(in) to the controller 420. The decouplingcapacitor C_(dec) is configured to absorb high frequency noise signalsassociated with the source of electrical power to protect the controller420.

In accordance with the aforementioned characteristics, the controller420 provides a signal (e.g., a pulse width modulated signal S_(PWM)) tocontrol a duty cycle and a frequency of the main and auxiliary switchesQ_(mn), Q_(aux) of the power train 410 to regulate the output voltageV_(out) thereof. The controller 420 may also provide a complement of thesignal (e.g., a complementary pulse width modulated signal S_(1-PWM)) inaccordance with the aforementioned characteristics. Any controlleradapted to control at least one switch of the power converter is wellwithin the broad scope of the present invention. As an example, acontroller employing digital circuitry is disclosed in U.S. Pat. No.7,038,438, entitled “Controller for a Power Converter and a Method ofControlling a Switch Thereof,” to Dwarakanath, et al. and U.S. Pat. No.7,019,505, entitled “Digital Controller for a Power Converter EmployingSelectable Phases Of A Clock Signal,” to Dwarakanath, et al., which areincorporated herein by reference.

The power converter also includes the driver 430 configured to providedrive signals S_(DRV1), S_(DRV2) to the main and auxiliary switchesQ_(mn), Q_(aux), respectively, based on the signals S_(PWM), S_(1-PWM)provided by the controller 420. There are a number of viablealternatives to implement a driver 430 that include techniques toprovide sufficient signal delays to prevent crosscurrents whencontrolling multiple switches in the power converter. The driver 430typically includes switching circuitry incorporating a plurality ofdriver switches that cooperate to provide the drive signals S_(DRV1),S_(DRV2) to the main and auxiliary switches Q_(mn), Q_(aux). Of course,any driver 430 capable of providing the drive signals S_(DRV1), S_(DRV2)to control a switch is well within the broad scope of the presentinvention. As an example, a driver is disclosed in U.S. PatentApplication Publication No. 2005/0168203, entitled “Driver for a PowerConverter and Method of Driving a Switch Thereof,” to Dwarakanath, etal., which is incorporated herein by reference. Also, an embodiment of asemiconductor device that may embody portions of the power conversioncircuitry is disclosed in U.S. Pat. No. 7,230,302, entitled “LaterallyDiffused Metal Oxide Semiconductor Device and Method of Forming theSame,” to Lotfi, et al., which is incorporated herein by reference, andan embodiment of an integrated circuit embodying power conversioncircuitry, or portions thereof, is disclosed in U.S. Pat. No. 7,015,544,entitled “Integrated Circuit Employable with a Power Converter,” toLotfi, et al., which is incorporated by reference.

Thus, a magnetic device, a power module and a method of manufacturethereof with readily attainable and quantifiable advantages have beenintroduced. Those skilled in the art should understand that thepreviously described embodiments of the magnetic device and power moduleare submitted for illustrative purposes only. In addition, otherembodiments capable of producing a magnetic device and a power modulewhile addressing compact, efficient and high density power modules,while being manufacturable at high volume and with lower cost than isachieved with the prior art are well within the broad scope of thepresent invention. While the magnetic device has been described in theenvironment of a power converter, the magnetic device may also beincorporated into other electronic devices, systems or assemblies suchas communication or computing devices or other power processing devices.

As mentioned above, the present invention provides a magnetic deviceincluding a magnetic core having a surface facing a conductive substrateand a conductive clip facing a surface of the magnetic core with ends ofthe conductive clip electrically coupled to the conductive substrate tocooperatively form a winding therewith about the magnetic core. As anexample, the present invention provides an inductor compatible withordinary manufacturing and packaging processes for power managementintegrated circuits. The inductor includes a magnetic core formed from abar of magnetic material adhered to conductive substrate (e.g., apatterned, conductive leadframe) and at least one conductive clip isplaced above the bar of magnetic material to complete the portion of theinductor winding above the leadframe. Preferably, the conductive clip ismade of copper, but other electrically conductive materials are wellwithin the broad scope of the present invention. The bar of magneticmaterial is adhered to the leadframe with a die attach adhesive, and theat least one conductive clip is soldered to the leadframe. The inductoris preferably encapsulated with plastic encapsulating compound includingan epoxy.

In an exemplary embodiment, the bar of magnetic material includes aceramic material such as a soft magnetic ferrite having manganese zincor nickel zinc ferrite. In a further exemplary embodiment, the bar ofmagnetic material is formed with a metallic alloy such as an iron cobaltalloy deposited via an electroplating process on a semiconductor orinsulating die such as a silicon die. The at least one conductive clipmay be soldered to the leadframe in a reflow soldering process.Additionally, a gap may be formed between the at least one conductiveclip and the bar of magnetic material. In accordance therewith, the gapis typically filled with plastic encapsulating compound. The integratedcircuit is also adhered to the leadframe. Preferably, the integratedcircuit is wire bonded (via, for instance, gold wires) to the leadframeto form electrical connections therebetween. Surface-mount componentsmay also be soldered to the leadframe.

In accordance with another aspect of the present invention, a magneticdevice, integrated circuit and surface-mount components are integratedto form an electronic device such as a power module or power managementintegrated circuit. In other aspects, the present invention providesmethods of forming the magnetic device and power module that takeadvantage of current practices in the field of power managementintegrated circuits.

For a better understanding of power converters, see “Modem DC-to-DCSwitchmode Power Converter Circuits,” by Rudolph P. Sevems and GordonBloom, Van Nostrand Reinhold Company, New York, N.Y. (1985) and“Principles of Power Electronics,” by J.G. Kassakian, M. F. Schlecht andG. C. Verghese, Addison-Wesley (1991). For a better understanding ofmagnetic devices, see “Soft Ferrites: Properties and Applications,” byE. C. Snelling, published by Butterworth-Heinemann, Second Edition,1989. The aforementioned references are incorporated herein by referencein their entirety.

Also, although the present invention and its advantages have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.For example, many of the processes discussed above can be implemented indifferent methodologies and replaced by other processes, or acombination thereof.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method of forming a magnetic device employablein a power module, comprising: providing a conductive substrateemployable in said power module; placing a magnetic core proximate saidconductive substrate with a lower surface adhered to an adhesive on saidconductive substrate, said magnetic core having an overall end-to-endlength and a continuous upper surface; placing a planar surface of aconductive clip above said continuous upper surface of said magneticcore, said conductive clip continuously spanning said overall end-to-endlength and said continuous upper surface of said magnetic core in aplane parallel to said conductive substrate; and electrically couplingends of said conductive clip to said conductive substrate to allow saidconductive clip to form a portion of a winding about said magnetic core.2. The method as recited in claim 1 wherein said conductive clip isabout 8 to 12 mils in thickness.
 3. The method as recited in claim 1wherein said continuous upper surface of said magnetic core issubstantially planar.
 4. The method as recited in claim 1 wherein saidmagnetic core is formed from manganese zinc ferrite.
 5. The method asrecited in claim 1 wherein said conductive substrate is a leadframe. 6.The method as recited in claim 1 wherein said adhesive is a die attachedadhesive.
 7. The method as recited in claim 1 wherein said ends of saidconductive clip are bent toward said conductive substrate about ends ofsaid magnetic core.
 8. The method as recited in claim 1 furthercomprising soldering said conductive clip to said conductive substrate.9. The method as recited in claim 1 further comprising providing a gapbetween said conductive clip and said magnetic core.
 10. The method asrecited in claim 1 further comprising encapsulating said magnetic core,said conductive clip and said conductive substrate.
 11. The method asrecited in claim 1 wherein said continuous upper surface of saidmagnetic core is rectangular.
 12. A method of forming a magnetic deviceemployable in a power module, comprising: providing a patterned,conductive leadframe employable in said power module; adhering amagnetic core formed from a bar of magnetic material to an adhesive onsaid conductive leadframe, said magnetic core having an overallend-to-end length and a continuous upper surface; placing a planarsurface of at least one conductive clip above said continuous uppersurface of said magnetic core, said at least one conductive clipcontinuously spanning said overall end-to-end length and said continuousupper surface of said magnetic core in a plane parallel to saidconductive leadframe; and soldering ends of said at least one conductiveclip to said conductive leadframe to allow said conductive clip to forma portion of a winding about said magnetic core.
 13. The method asrecited in claim 12 wherein said bar of magnetic material is formed frommanganese zinc ferrite.
 14. The method as recited in claim 12 furthercomprising forming terminals for external electrical connections bycreating leadframe fingers in said conductive leadframe.
 15. The methodas recited in claim 12 further comprising electrically coupling portionsof said conductive leadframe with at least one wire bond.
 16. The methodas recited in claim 12 wherein said ends of said at least one conductiveclip are bent toward said conductive leadframe about ends of saidmagnetic core.
 17. The method as recited in claim 12 further comprisingproviding a gap between said magnetic core and said at least oneconductive clip.
 18. The method as recited in claim 12 furthercomprising providing a gap between said magnetic core and said at leastone conductive clip and further comprising substantially filling saidgap with an encapsulant.
 19. The method as recited in claim 12 furthercomprising encapsulating said magnetic core, said at least oneconductive clip and said conductive leadframe.
 20. The method as recitedin claim 12 further comprising encapsulating said magnetic core, said atleast one conductive clip and said conductive leadframe with an epoxyencapsulant.
 21. The method as recited in claim 12 wherein said magneticdevice is an inductor.